1. Field of the Invention
The present invention relates to position control devices and in particular active control positionable tables used for precise positioning of parts that are being machined or worked on.
2. Description of the Prior Art
In grinding and machining operations which require precise positioning, various tables have been advanced for use. Generally speaking the present tables comprise slides which are difficult to monitor precisely and difficult to maintain in a precise position due to backlash in the mounting. For example, U.S. Pat. No. 4,229,909 shows a tool grinding machine which has a support table which will slide in and out relative to the grinding wheel and also can be rotated about a pivot. A spring is controlled for maintaining a load on the tool grinding machine in an axial direction, but it does move a sliding connection which will cause backlash, and it does not include means for an active control of a table that has a friction free pivot for the table.
U.S. Pat. No. 3,916,571 shows a cam controlled machine tool for machining parts of various configurations. While it includes a typical control system having thumb wheel input switches and digital controls for providing an output, the programming does rely upon cams for moving the support table in a desired path of movement to produce the contour that is needed in the completed part.
U.S. Pat. No. 4,425,061 is a tool setting device for a machining center utilizing numerical controls, and a gauge unit using detectors for providing position signals, and for indicating arrival of the tool at a desired location. Thus, the device shows a control with feedback signals, but does not include a part support table operating on a friction free pivot as with the present device.
U.S. Pat. No. 4,419,612 illustrates a electromechanical internal grinding machine for controlling slides for feeding parts into a grinding machine. Screw actuators are used for transmitting the control commands, which again have backlash, and the use of backlash free mounting supports for the work table is not disclosed.
U.S. Pat. No. 4,441,103 shows a vibration sensing transducer for machine tools, which is a piezoelectric vibration detecting member having suitable controls for stopping the rotation or travel of a tool and causing the feed of the workpiece to stop if an unusual vibration is sensed. It also provides a way of utilizing a rapid in-feed, which will change instantly to a more satisfactory grinding feed rate.
U.S. Pat. No. 4,251,760 shows a gauging and tool control system for production of identical parts utilizing a closed loop feedback control, but it does not include a table of the type that has a friction free support hinge. It does, however, show a typical prior art control system for controlling motions of a machine tool.
U.S. Pat. No. 3,665,652 is a control system for a grinder that has a sensor for generating a signal that represents the dimensional characteristics of the workpiece and has means for providing signals indicating the rate of removal of material from the workpiece. It is not used in connection with a table that controls the position of the workpiece precisely with respect to a reference surface of the grinding wheel or tool that is being used.
U.S. Pat. No. 4,140,998 shows a high accuracy position indicator using an LVDT as a position transducer and in particular relates to circuitry with two position rectifiers to cancel out the effects of input voltage frequency fluctuation. This, again, shows a typical existing LVDT application, and relates to providing a very high accuracy LVDT.
U.S. Pat. No. 2,600,550 illustrates a taper control indicator for controlling a grinder which is a manual adjustment system using a visual display in substantially different sensing elements than that used with the present device.
U.S. Pat. No. 3,554,064 shows a system utilizing a thermally insensitive element, such as a rod which is anchored at one end to a body and a strain guage controlled heater or cooler that brings the temperature of the controlled device to a value which results in maintenance of a predetermined length of the part. A slide, is again used, which has backlash in its mounting.
An electronic swivel control is shown in U.S. Pat. No. 2,880,407, and this device does include a pivoting device using a conventional pivot that does have backlash. In addition, the device is used only for setting the position before or at the start of a machining process and does not provide active adjustment or control during machining.
Thus, in the prior art, the problems of providing a precise active control system exist in the machine tool industry.